const string field vs "typed" string

Question

i have a little function that goes like this:

void Bar(string s)
{
*/ do somthing with the string here.*/
}

void Foo()
{
    Bar("Hello");
}

if i look at the IL output, it gives me the following:

.method private hidebysig instance void Foo() cil managed
{
    .maxstack 8
    L_0000: ldarg.0 
    L_0001: ldstr "Hello"
    L_0006: call instance void TestApp.MainWindow::Bar(string)
    L_000b: ret 
}

now i thought i'd replace it with a const string field for it.

const string str= "Hello";
void Foo()
{
    Bar(str);
}

that translates TO THE EXACT SAME IL snippet.

now my question is which one to use?

Foo("Hello"); or Foo(cHello);

Thank you for your help!

--------------EDIT-------------------
To be more specific, i use this for Logging purposes to add a prefix to a message: AND it would only appear once in code!

so it looks more like this:

void LogDebug(string msg)
{
    Log("[DEBUG]", msg)
}
void Log(string pre, string msg)
{
    // generates an output in form of
    // pre + msg
}

:)

Jon · Accepted Answer · 2013-03-14 11:13:15Z

5

The answer should be obvious: since the IL is the same, use whatever works best based on purely source-code considerations.

In general, this means going with the const string in order to not have a magic value appear in your Foo method. If the constant is used just once this might not sound very convincing, but if there is even a possibility of using it more than once in the future then DRY is pretty much a shotgun argument.

Update:

In this specific case (debugging output, constant is guaranteed to be used only once) I don't think that a constant provides any value. I 'd hardcode the string literal.

edited Mar 14, 2013 at 11:13

answered Mar 14, 2013 at 10:59

Jon

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Habib · Accepted Answer · 2013-03-14 10:58:48Z

3

const get replaced at compile time in the code. Its better if you use the const string instead of hard coded string since it makes them easy to maintain.

answered Mar 14, 2013 at 10:58

Habib

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Community · Accepted Answer · 2017-04-12 07:31:20Z

0

(1) Use const string for private or internal code if it would make the code more readable or you would have the same string more than once.

(2) DO NOT PUBLICLY EXPOSE CONSTS. Use properties instead. (Particularly with regard to strings.)

The reason for that is it tightly binds the const into the assemblies that reference it.

See here for more discussion about that point:

https://softwareengineering.stackexchange.com/questions/132747/is-having-public-constants-bad

edited Apr 12, 2017 at 7:31

CommunityBot

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answered Mar 14, 2013 at 11:03

Matthew Watson

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4 Comments

oleksii Over a year ago

-1 for capital letters and incorrect statement. Constant fields are widely used when there is a need for them, see Math.PI for an example.

Jon Over a year ago

@oleksii: That's not quite right. We are not talking about public const here, but if we did then you 'd have to be pretty sure that the value of the constant remains fixed forever. Math.PI fits that description, but your own custom constant might not.

Corak Over a year ago

There are few things more frustrating than: I changed the constant in first.dll, why does method in second.dll still work with the old value?

Matthew Watson Over a year ago

@oleskii: Mathematical and physical consts are a special case, of course - but there are very few of them (e, pi, the golden ratio, G and so on), but the general rule certainly should be that you do not make consts public. See here for some discussion: programmers.stackexchange.com/questions/132747/…

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